The statements in this section merely provide background information related to the present invention and may or may not constitute prior art.
A typical automatic transmission includes an electronically controlled hydraulic control circuit or system that uses a hydraulic fluid to actuate torque transmitting mechanisms, as well as to lubricate and cool the transmission. The hydraulic fluid is typically stored in a fluid reservoir, or sump, located at a bottom of the transmission. A pump connected to the sump is used to draw the hydraulic fluid from the sump and communicate the hydraulic fluid throughout the hydraulic control system.
In order to prevent damage to the control system due to unwanted contaminants that may be present in the hydraulic fluid, a filter is generally disposed in the sump and is connected to the pump. The filter includes a filter element surrounded by a filter body having an inlet for incoming hydraulic fluid and an outlet for outgoing hydraulic fluid. The filter removes the contaminants from the hydraulic fluid prior to entering the pump.
However, it is desirable that the volume of hydraulic fluid in the sump be large enough so that the filter inlet for incoming fluid is submerged in the hydraulic fluid in order to prevent air from being drawn into the filter, thus leading to air entrainment within the hydraulic fluid. Entrained air within the hydraulic fluid, in turn, reduces the control, cooling, and lubrication effectiveness of the hydraulic fluid.
Existing sump filter designs and manufacturing tolerances may lead to the filter body and filter inlet to move up and away from the bottom of the sump. The accumulated system manufacturing tolerances at the filter inlet may be, for example, on the order of 7-8 mm. As a result, the volume of hydraulic fluid stored in the sump must by increased by a corresponding amount to prevent the filter inlet from lifting out of the hydraulic fluid due to manufacturing tolerances and therefore drawing air into the filter. However, this increased volume of hydraulic fluid adds to the vehicle mass, cost, and packaging, and increases the burdens of transmission hydraulic fluid management on the system. These consequences of additional hydraulic fluid volume also negatively affect vehicle acceleration, braking, and maneuverability. Accordingly, there is a need for a transmission sump filter assembly that reduces movement of the filter inlet opening due to manufacturing tolerances in order to minimize the volume of hydraulic fluid within the sump.